1. Field of the Invention
The invention relates to a method and apparatus for separating slag and nonmetallic particles from molten metal during teeming operations. Specifically, the invention provides a meltable dam which retains the slag and nonmetallic particles in a tundish while molten metal is transferred through the tundish.
2. Description of the Invention Background
In processes for making steel and other alloys, metals are typically heated to a molten state and transferred from one vessel to another. In particular, the molten metal is often transferred from a ladle into a tundish, or multiple tundishes, and then transferred from the tundish into molds such as ingot molds. This operation of transferring the molten metal is called teeming.
In a typical teeming operation contaminant materials such as slag and nonmetallic particles are transferred along with the molten metal. The slag and nonmetallic particles may interfere with the teeming operation and are detrimental to the quality of the desired metal product which is formed in the ingot molds.
For example, in a vacuum induction melt (VIM) teeming operation the molten metal is top poured from a furnace into a tundish. The molten metal then flows from the tundish through flow channels which direct the molten metal to another vessel, such as molds or additional tundishes. Slag and nonmetallic particles usually occur in the molten metal and float on top of the molten metal because they are less dense than the molten metal. Typically, the slag and nonmetallic particles enter the tundish and subsequent flow channels with the first flow of the molten metal because the molten metal is top poured during VIM teeming operations.
The transfer of the slag and nonmetallic particles along with the molten metal creates several problems during the teeming operation. First, the slag and nonmetallic particles may block the various flow channels through which the molten metal must flow. In particular, slag and nonmetallic particles have been known to block the nozzles through which the molten metal leaves the tundish during VIM teeming operations. This may cause an excess amount of molten metal to remain in the tundish because the molten metal cannot properly flow from the tundish. In addition, the presence of the slag and nonmetallic particles in the first flow of the molten metal will tend to reduce the desired quality of cast metal because these nondesired materials are carried through to the molds.
Thus, a need exists for a method and apparatus to prevent slag and nonmetallic particles from being carried with the first flow of molten metal through a tundish into the molds during a teeming operation. More particularly, a need exists for retaining the slag and nonmetallic particles in a tundish during a VIM teeming operation until the molten metal flows through the tundish into the molds.